The present invention relates generally to the field of electricity switching, and more particularly to high current capacity electrical contactors.
Such contactors generally comprise a high current switch with two or more electrically conductive contacts, at least one of which is movable. When the contacts touch or close an electrical communication path is established through which high electrical currents may flow. A contactor furthermore generally comprises an actuator, which is typically of a solenoid type with a wound coil. The actuator serves to influence the position of the movable contact. As such, a relatively small amount of electrical power applied to the solenoid coil can influence the movable contact to touch/close or separate/open from the other contact(s). Most typical high current electrical contactors are configured such that when the solenoid actuator member is deactivated, the contacts are open. This is commonly referred to as a normally open (NO) contactor.
Generally, the contacts of a NO contactor can be structured to either permissively make or be forced to make an electrical connection between one or more terminals through which high current may flow. In either of these structures, the coil must be activated to establish electrical communication between two or more high current terminals. Stated conversely, in both structures, when the coil is deactivated, or in its free state, the provided terminals are separated and are not in electrical communication.
The distinction between a NO contactor of the permissive-make configuration and one of the forced make configuration is generally not evident from external observation nor simply through observing electrical switching behavior, because either configuration will close upon activation. Upon internal examination, however, the types can be distinguished based upon the relation between the mechanical engagement of the actuator with the movable contact and the electrically communicative engagement of the contacts. In a permissive-make NO contactor, the contacts are under a bias that will cause them to close or make contact when separated from the actuator portion of the contactor. In other words, activation of the contactor allows or permits the contacts to close under the bias force. Conversely, the contacts open when the movable contact is mechanically engaged by the actuator. In contrast, in a forced make NO contactor, the contacts are under a bias that will cause them to be open when separated from the actuator or when the actuator is deactivated. Conversely, the contacts close when the movable contact is mechanically engaged by the actuator. In other words, activation of the contactor forces the contacts to close under the mechanical engagement of the actuator with the movable contact, overcoming the biasing force.
Thus, a permissive-make contactor generally refers to a contactor that must be activated to make or achieve an electrical coupling between two or more terminals. Stated conversely, when a permissive-make contactor is deactivated, or in its free state, the provided terminals are in electrical isolation.
It is a well known problem that the contacts of electromagnetically activated contactors undergo severe stresses during use. For example, when current carrying contacts are separated, electrical arcing is likely to occur, thereby decreasing the life of the contacts by wearing the contact surfaces. Therefore, sufficient force must be used in separating the contacts so that the arcing is minimized in time. That is, the less time the arc exists, the less wear on the contacts per switching cycle. In permissive-make contactors, the separation of current carrying contacts is achieved largely by a biasing member, and the force applied to the movable contact is directly related to same. Thus, to achieve a fast break of the electrical communication, a sufficiently forceful biasing mechanism must be used. Conversely, when separated contacts are engaged, the contacts have been known to bounce, thus creating an arc and leading to further wear on the contacts. Contact bouncing is the leading cause of break arc, and it may even lead to hard destructive welding of the electrical contacts under certain conditions.
Therefore, the art of electrical contactors would benefit from a device that exhibits improved electrical communication making and/or breaking actions.